For over 40 years, various private firms and government agencies have been working to develop a reliable liquid propellant gun. An excellent historical summary of liquid propellant gun research was published by W. F. Morrison, J. D. Knapton and M. J. Bulman, Liquid Propellant Guns, Gun Propulsion Technology of Volume 109, 1988, which has been incorporated herein by reference in its entirety. This publication has been incorporated to provide historical background information and is to be regarded as nonessential subject matter. One of the primary attractions to liquid propellant guns are their ability to store projectiles and propellant very compactly with little wasted space. Charges may be varied on an as needed basis to suit the conditions at the time of projectile firing and the propellant can be stored in a remote safe location and is simply transported to the combustion chamber when required.
A wide variety of propellants have been developed over the years. Work has been done with liquid gaseous mixtures; bi-propellants such as a hydrocarbon fuel and an oxygen containing agent, such as hydrogen peroxide, separately metered into and mixed within combustion chamber; and monopropellants, such as hydrazine based propellants or hydroxyl ammonium nitrate (HAN) propellants. While there is still room for improvement in propellant technology, the primary drawback to commercialization of liquid propellant guns is the lack or ability to control combustion sufficiently to achieve ballistic variability consistent with conventional guns using a granular solid propellant.